Photocatalytic filter, method for manufacturing the same, and method for reactivating the same

ABSTRACT

The devices, systems and techniques disclosed in this patent document include photocatalytic filter devices and can be used to provide a method for manufacturing a photocatalytic filter with improved adhesion. In addition, the present disclosure of this patent document includes technology to provide a method for reactivating a photocatalytic filter. Using the disclosed techniques, even if a photocatalytic filter is contaminated, the contaminated photocatalytic filter is easily reactivated while maintaining improved adhesion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority and benefits of Provisional ApplicationSer. No. 62/046,114 filed on Sep. 4, 2014, and Chinese PatentApplication No. 201510096993.1 filed on Mar. 4, 2015. The entiredisclosures of the above applications are incorporated by reference aspart of this document.

TECHNICAL FIELD

This patent document relates to a photocatalytic filter device and atechnique of manufacturing and reactivating a photocatalytic filter.

BACKGROUND

As used herein, the term “photocatalytic reaction” refers to reactionsthat use photocatalytic materials such as titanium dioxide (TiO₂) or thelike. Known photocatalytic reactions include photocatalytic degradationof water, electrodeposition of silver and platinum, degradation oforganic materials, etc. Also, there have been attempts to apply suchphotocatalytic reactions to new organic synthetic reactions, ultrapurewater production and the like.

Toxic gases or offensive odor substances, such as ammonia, acetic acidand acetaldehyde, which are present in air, are degraded by theabove-described photocatalytic reactions, and air purification devicesbased on such photocatalytic reactions can be used semi-permanently ifthey have a light source (e.g., a UV light source) and a filter coatedwith a photocatalytic material. When the photocatalytic efficiency ofthe photocatalytic filter has reduced, the filter can be reactivated torestore its photocatalytic efficiency, and then it can be reused. Thus,it can be said that the photocatalytic filter is semi-permanent.

For example, when a UV LED lamp is used as a UV light source, it isadvantageous over a conventional mercury lamp or the like in that the UVLED lamp is environmentally friendly. The UV LED lamp does not requiretoxic gas and is highly efficient in terms of energy consumption, andallows various designs by virtue of its small size.

However, unlike conventional filters such as the pre-filter or HEPAfilter, which physically collect large dust particles when air passestherethrough, the photocatalytic filter is configured such that toxicgases adsorbed on the surface of the filter during the passage of airthrough the filter are degraded by radicals such as OH⁻, generated bythe photocatalytic reaction. Thus, toxic gases in air degraded duringthe passage of the air through the catalytic filter are not completelydegraded, but a portion of the toxic gases is degraded. In other words,the amount of degraded toxic gases in air is gradually increased whilethe air passes several times through the photocatalytic filter.

Thus, the photocatalytic efficiency of the photocatalytic filter islinked directly with the air cleaning ability of the photocatalyticfilter. Toxic gas in a space that uses an air cleaner having highphotocatalytic efficiency is degraded faster than toxic gas in a spacethat uses an air cleaner having the same size and structure but having arelatively low photocatalytic efficiency.

However, if a photocatalytic material in a photocatalytic filter iscontaminated, the photocatalytic efficiency will be reduced, and thefilter cannot exhibit its function. In this case, the photocatalyticfilter generally needs to be replaced. There have been studies onwhether a photocatalytic filter can be washed, but the results of thestudies mainly indicated that washing of the photocatalytic filter isundesirable, because the washing process is complex and thephotocatalytic filter is not easily washed.

SUMMARY

Various embodiments provide an easily regenerable photocatalytic filter,a method for manufacturing the same, and a method for reactivating thesame.

In an embodiment, a method for manufacturing a photocatalytic filter isprovided to include: dispersing a photocatalytic material; coating asupport with the dispersed photocatalytic material; drying the coatedsupport; and sintering the dried support.

In some implementations, the photocatalytic material may includetitanium dioxide (TiO₂).

In some implementations, the support may include a porous ceramicmaterial.

In some implementations, the sintering may be performed at a temperatureof 400 to 500° C. for 1-3 hours, preferably 2-3 hours.

In another embodiment, a photocatalytic filter is provided to include aporous ceramic support, and dispersed TiO₂ nanoparticles coated on thesupport.

In some implementations, the TiO₂ nanoparticles coated on the porousceramic support are those sintered for from one to three hours at atemperature between 400° C. and 500° C.

In some implementations, the photocatalytic filter may comprise aplurality of adjacent parallel cells that form an air flow path in adirection facing UV LED for photocatalytic activation.

In some implementations, the photocatalytic filter comprises a pluralityof adjacent parallel cells that form an air flow path in a directionfacing UV LED for photocatalytic activation.

In some implementations, the photocatalytic filter has a height of 2 to15 mm.

In some implementations, a frame between the cells has a thickness of0.3 to 1.2 mm.

In some implementations, each of the cells has a width of 1 to 4 mm.

In some implementations, the cells has a density of 30 to 260cells/inch².

In still another embodiment, a method of reactivating a photocatalyticfilter is provided to include: treating a contaminated photocatalyticfilter with boiling water, and/or microwaving the treated photocatalyticfilter, wherein the photocatalytic filter includes a support coated withdispersed TiO₂ nanoparticles.

In some implementations, the support includes porous ceramic, and theTiO₂ nanoparticles coated on the support are those sintered for from oneto three hours at a temperature between 400° C. and 500° C.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing an arrangement of an exemplaryphotocatalytic filter and a UV LED substrate.

FIG. 2 is a top view of an exemplary photocatalytic filter.

FIG. 3 is a graph showing the change in removal rate of acetaldehydewith a change in the height of a photocatalytic filter.

FIG. 4 is a graph showing the change in removal rate of acetic acid witha change in the height of a photocatalytic filter.

FIG. 5 is a photograph showing the state of a conventionalphotocatalytic filter and a photocatalytic filter provided according tothe present disclosure.

FIGS. 6 and 7 are graphs showing the transmittance of water boiled witheach of various filters added thereto.

FIG. 8 is a graph showing the results of cleaning air by filtersreactivated using boiling water.

FIG. 9 is a graph showing the results of cleaning air by aphotocatalytic filter before and after contamination of the filter.

FIG. 10 is a graph showing the results of cleaning air by aphotocatalytic filter before and after contamination of the filter andafter reactivating the filter by treating the filter with boiling water.

FIG. 11 is a graph showing the results of cleaning air by aphotocatalytic filter before and after contamination of the filter andafter reactivating the filter by treating the filter with boiling waterand microwaving the treated filter.

DETAILED DESCRIPTION

The devices, systems and techniques disclosed in this patent documentprovide photocatalytic filter devices and a method of manufacturing aphotocatalytic filter with improved adhesion.

In addition, the present disclosure of this patent document includestechnology to provide a method for reactivating a photocatalytic filter.Using the disclosed techniques, even if a photocatalytic filter iscontaminated, the contaminated photocatalytic filter is easilyreactivated while maintaining improved adhesion.

The devices, systems and techniques in this patent document aredisclosed by examples in the following descriptions and claims.

Hereinafter, embodiments of the disclosed technology will be describedin detail with reference to implementation examples, including thoseillustrated in the accompanying drawings.

The following embodiments are provided by way of examples so as tofacilitate the understanding of various implementations of the disclosedtechnology to those skilled in the art.

Accordingly, the present disclosure is not limited to the embodimentsdisclosed herein and can be implemented in different forms. In thedrawings, widths, lengths, thicknesses, and the like of elements may beexaggerated for convenience and illustrative purposes.

Photocatalytic Filter—Device

Hereinafter, an example of a photocatalytic filter is provided. Thephotocatalytic filter includes a support, and dispersed TiO₂nanoparticles coated on the support.

The support may include a metal, activated carbon, or ceramic. In oneimplementation, a porous ceramic honeycomb support may be used as thesupport. In this case, the porous ceramic honeycomb support helps TiO₂nanoparticles to permeate the ceramic pores during the coating process.Further, TiO₂ nanoparticles are anchored through the drying process thatwill be discussed later in detail, and thus, adhesion of the TiO₂nanoparticles to the support is enhanced.

If a metal material is used as the support, TiO₂ nanoparticles are notas easily attached to the photocatalytic support as the porous ceramichoneycomb support. Further, although activated carbon has pores, theactivated carbon may be easily damaged during the sintering process.

As will be discussed later in detail, the support may be coated withdispersed TiO₂ nanoparticles, thereby providing a photocatalytic filterwith improved adhesion.

FIG. 1 is a perspective view showing the arrangement of thephotocatalytic filter 80 and the UV LED substrate 55, and FIG. 2 is atop view of the photocatalytic filter 80.

Referring to FIG. 1, the UV LED 56 for sterilization is disposed on thecentral portion of the UV LED substrate 55, and three UV LEDs 57 forphotocatalytic activation are disposed around the UV LED 56. In someimplementations, the UV LEDs 57 for photocatalytic activation willirradiate UV light toward the photocatalytic filter 80.

As shown in FIG. 2, the photocatalytic filter 80 includes a catalystportion 81 obtained by sintering TiO₂ (titanium dioxide) coated on aceramic porous material having a check lattice pattern, and an elasticbumper 82 covering the side of the catalyst portion.

FIG. 3 is a graph showing removal rates of acetaldehyde of twophotocatalytic filters that have different heights (h), and FIG. 4 is agraph showing removal rates of acetic acid of two photocatalytic filtersthat have different height (h).

The results of the experiment indicated that, in the case of thephotocatalytic filter having the shape shown in FIG. 2, the surface areaof the photocatalyst, which increases due to the thickness (t) of theframe between the cells of the photocatalytic filter, did notsubstantially influence the deodorization efficiency of thephotocatalytic filter, but the height (depth) of the photocatalyticfilter influenced the inner wall area of the internal air flow path,thus directly influencing the area of contact with air.

Thus, it could be seen that, when the height of the photocatalyticfilter was 5-10 mm, the deodorization efficiency of the photocatalyticfilter was the highest. In addition, when the height decreases to 2 mmor less, the photocatalytic filter is difficult to use, due to its weakstrength, and when the height is 15 mm or more, air resistance merelyincreases, UV light does not reach the rear portion of thephotocatalytic filter or the intensity thereof becomes very weak, andthus only the cost increases without increasing the deodorizationefficiency.

Also, it could be seen that, when the width (g) of each cell 83 was 2mm, the air resistance did not increase, and the rate of shadowed areaof the inner wall of the photocatalytic filter, which is generated bythe shape of the filter itself blocking UV light irradiated thereto, wasnot high, suggesting that the cell width of 2 mm is most suitable formaximizing the rate of UV light irradiated area of the inner wall of thephotocatalytic filter. Meanwhile, when the cell width decreased to 1 mmor less, the air resistance increased, and the amount of UV lightreaching the inner wall decreased, suggesting that the efficiency ofdeodorization was low. In addition, when the cell width was 4 mm ormore, the whole area of the inner wall decreased due to low celldensity, which suggests that the efficiency of deodorization was low.

Regarding the density of cells in view of width (g) of each cell abovementioned, when the density of cells was lower than 30 cells/inch² orless, that is, the cell width increased to 4 mm or more, the area of theinner wall decreased. This indicates that the efficiency ofdeodorization was low. When the density of cells was 260 cells/inch² ormore, that is, the cell width decreased to 1 mm or less, the airresistance increased and the amount of UV light reaching the inner walldecreased. This indicates that the efficiency of deodorization was low.When the density of cells was about 100 cells/inch², the air resistancedid not increase, and the rate of shadowed area of the inner wall of thefilter, which is generated by the shape of the filter itself blocking UVlight irradiated thereto, was not high. This suggests that theefficiency of deodorization was the highest.

The results of an experiment on the thickness (t) of the cell frameindicated that, when the frame thickness was 0.3 mm or less, the TiO₂layer became too thin, and thus the photocatalytic efficiency decreasedand the strength was insufficient. When the frame thickness was 1.2 mmor more, the material cost increased without increasing thephotocatalytic efficiency. In addition, the photocatalytic efficiencywas the highest when the frame thickness was 0.6 mm.

Photocatalytic Filter—Fabrication Process

Hereinafter, an example of a method of manufacturing a photocatalyticfilter will be discussed.

The photocatalytic filter may be provided by dispersing titanium dioxide(TiO₂) nanoparticles, coating a support with the dispersed TiO₂nanoparticles, drying the coated support and sintering the driedsupport.

As one example, the dispersing process is performed using P25 TiO₂nano-powders commercially available from Evonik Degussa. For example,P25 TiO₂ nano-powders may be added into water into which silicondispersing agent with a concentration between 0.1 and 10% may bedissolved. After dispersing P25 TiO₂ nano-powders using a mill, a solidTiO₂ nano solution with a concentration from 20 to 40% may be obtained.The dispersing agent including one or more types of components may beused.

During the coating process, if the porous ceramic honeycomb support isselected, the porous ceramic honeycomb support is dip-coated with theprepared TiO₂ dispersion liquid. At the time of dip-coating, one to fiveminutes suspension may be applied such that TiO₂ dispersion liquid issufficiently absorbed by the pores of the porous ceramic honeycombsupport.

The drying process may be performed for a predetermined time in acondition that the coated support is maintained at a predeterminedtemperature. In one implementation, if the porous ceramic honeycombsupport is selected, the coated porous honeycomb ceramic support may bemaintained in a drying unit at a temperature between 150° C. to 200° C.for three to five minutes.

The sintering process may be performed by maintaining the dried supportat a predetermined temperature for a predetermined time. In oneimplementation, if the porous ceramic honeycomb support is selected, thesintering process may be performed for from two to three hours atbetween 400° C. and 500° C. Upon our experiments, if the sinteringtemperature is lower than 300° C., the coated TiO₂ photocatalyst isseparated easily from the support. If the sintering temperature ishigher than 500° C., the crystal structure of the coated TiO₂photocatalyst changes and thus, the photocatalyst activationdeteriorates. Thus, in order to provide a photocatalytic filter withimproved adhesion and photocatalyst activation, the sintering processmay be performed at between 400° C. and 500° C.

Reactivated Photocatalytic Filter

FIG. 5 shows the results of an experiment conducted to examine theadhesion of a catalytic material to a support in a TiO₂ photocatalyticfilter. In the experiment, each of sintered and unsinteredphotocatalytic filters was dipped in distilled water, and thensonicated.

As can be seen in FIG. 5, unlike the case of the sintered photocatalyticfilter, TiO₂ attached to the unsintered photocatalytic filter was elutedinto water by sonication.

FIG. 6 shows the transmittance of distilled water, which was measured atvarious wavelengths in each of the following cases: sonicating distilledwater only; adding to distilled water a porous ceramic material notcoated with a TiO₂ photocatalytic material and then sonicating thedistilled water; adding to distilled water a porous ceramic materialcoated with a TiO₂ photocatalytic material and sintered and thensonicating the distilled water; and adding to distilled water a porousceramic material coated with a TiO₂ photocatalytic material but notsintered and then sonicating the distilled water. The transmittance wasmeasured by UV-Vis Spectroscopy (detector: Analytik Jena).

As can be seen in FIG. 6, the transmittance of the water containing theporous ceramic material, which was coated with the TiO₂ photocatalyticmaterial and sintered, was nearly similar to that of distilled water.This suggests that the photocatalytic material had excellent adhesion tothe porous ceramic material, and that the photocatalytic material wasnot substantially eluted.

This result indicates that the photocatalytic filter manufacturedaccording to the method of the present disclosure maintains the adhesionof the photocatalytic material to the surface of the photocatalyticfilter even when the photocatalytic filter is sonicated.

FIG. 7 shows the transmittance of water measured as a function ofsonication time in each of the following cases: sonicating distilledwater only; adding to distilled water a porous ceramic material notcoated with a TiO₂ photocatalytic material and then sonicating thedistilled water; and adding to distilled water a porous ceramic materialcoated with a TiO₂ photocatalytic material and sintered and thensonicating the distilled water.

As can be seen in FIG. 7, in the case in which the porous ceramicmaterial, coated with the TiO₂ photocatalytic material and sintered, wasadded to distilled water and sonicated, the transmittance of thedistilled water showed a tendency to decrease as the sonication timeincreased, but this decrease in transmittance was not visuallydistinguishable from distilled water only.

FIG. 8 shows the results of measuring the acetaldehyde removalactivities of the two samples (see the arrows in FIG. 7) showing thegreatest difference in transmittance therebetween among the samples ofFIG. 7, after naturally drying the two samples for use as photocatalyticfilters. As can be seen in FIG. 8, there was little or no difference inphotocatalytic activity between the two samples showing differenttransmittances as shown in FIG. 7.

The reactivative characteristics of the TiO₂ nanoparticle-coatedphotocatalyst are shown in FIG. 9 to FIG. 11. The two graphs (markedFilter 1 and Filter 2) on FIG. 9 show two sets of experiments toirradiate a contaminated TiO₂ nanoparticle coated filter and a freshuncontaminated TiO₂ nanoparticle coated filter, by using a UV LED sourcefor a period of 3 hours so as to remove acetaldehyde. In both Filter 1and Filter 2 figures, the contaminated TiO₂ nanoparticle coated filteris contaminated with chemicals including formaldehyde, acetic acid, NH₃,toluene, CH₃—S—SCH₃, or commercial air freshener (aromatic).

As can be seen in FIG. 9, the uncontaminated filter normally degradedacetaldehyde (see the plot marked as Fresh TiO₂ in FIG. 9). However,when an experiment was performed using a photocatalytic filtercontaminated after used in the above-described acetaldehyde removalexperiment, it could be seen that the amount of acetaldehyde did notdecrease (see the plot marked as contaminated TiO₂ in FIG. 9),suggesting that the photocatalytic activity of the filter was poor.

FIG. 10 shows reactivation of the contaminated TiO₂ nanoparticle coatedon filters after being treated with boiling water and FIG. 11 showsreactivation of the contaminated TiO₂ nanoparticle coated on filtersafter being treated a combination of boiling water and microwaveexposure. The reactivity properties of the contaminated TiO₂nanoparticle coated on filters are compared against fresh uncontaminatedTiO₂ nanoparticle coated on filters.

As can be seen in FIG. 10, when the contaminated filter was treated withboiling water, the function of the filter was significantly restored. Asshown in FIG. 11, when the contaminated filter was treated with boilingwater and then microwaved, the filter was reactivated so that it wouldshow performance nearly similar to that of its original state.

As described above, the present disclosure provides the photocatalyticfilter including the photocatalytic material attached securely to thesupport. Thus, the photocatalytic material is not detached from thephotocatalytic filter during reactivation, and thus can be repeatedlyreactivated. Thus, the photocatalytic filter can be usedsemi-permanently. This is different from The conventional photocatalyticfilters where the reactivation via boiling cannot be achieved since thephotocatalytic material is not so securely attached to the support as itis not eluted from the support into water while being treated withboiling water.

In addition, according to the present disclosure, the photocatalyticfilter can be reactivated in a simple manner without using a troublesomewashing process.

Though only a few embodiments, implementations and examples aredescribed, other embodiments and implementations, and variousenhancements and variations can be made based on what is described andillustrated in this document.

What is claimed is:
 1. A method of manufacturing a photocatalyticfilter, the method including: dispersing a photocatalytic material;coating a support with the dispersed photocatalytic material; drying thecoated support; and sintering the dried support to provide a catalystportion of the photocatalytic filter; wherein the catalyst portion has aheight between 8 to 10 mm, wherein the photocatalytic filter includescells formed in the catalyst portion and provides an air flow path in adirection facing UV LED for photocatalytic activation, wherein a framebetween the cells has a thickness of 0.3 to 1.2 mm, and each of thecells has a width of 2 to 4 mm.
 2. The method of claim 1, wherein thephotocatalytic material includes titanium dioxide (TiO₂).
 3. The methodof claim 1, wherein the support includes porous ceramic.
 4. The methodof claim 1, wherein the sintering is performed for from one to threehours at a temperature between 400° C. and 500° C.
 5. A photocatalyticfilter, including: a catalyst portion including a porous ceramic supportand dispersed TiO₂ nanoparticles coated on the porous ceramic support;and a bumper covering a side of the catalyst portion; and cells formedin the catalyst portion and providing an air flow path in a directionfacing UV LED for photocatalytic activation, wherein the photocatalyticfilter has a height between 8 to 10 mm, wherein a frame between thecells has a thickness of 0.3 to 1.2 mm, and wherein each of the cellshas a width of 2 to 4 mm.
 6. The photocatalytic filter of claim 5,wherein the TiO₂ nanoparticles are sintered for from one to three hoursat a temperature between 400° C. and 500° C.
 7. The method of claim 1,further comprising adding distilled water to the photocatalytic filter.8. The method of claim 1, further comprising, after the covering of theside of the support: sonicating the photocatalytic filter.
 9. The methodof claim 8, wherein the photocatalytic material maintains an adhesion tothe support while the photocatalytic filter is sonicated.